Refractory metal silicide nanoparticle ceramics

ABSTRACT

Particles of a refractory metal or a refractory-metal compound capable of decomposing or reacting into refractory-metal nanoparticles, elemental silicon, and an organic compound having a char yield of at least 60% by weight are combined to form a precursor mixture. The mixture is heating, forming a thermoset and/or metal nanoparticles. Further heating form a composition having nanoparticles of a refractory-metal silicide and a carbonaceous matrix. The composition is not in the form of a powder

This application claims the benefit of U.S. Provisional Application No.62/331,069, filed on May 3, 2016. The provisional application and allother publications and patent documents referred to throughout thisnonprovisional application are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure is generally related to metal silicide ceramics

DESCRIPTION OF RELATED ART

Refractory metal silicides are needed and attractive because of theirultra-high melting temperatures and excellent oxidation resistance.Refractory metal silicide ceramics are some of the highest temperaturematerials (m. p. >2000° C.) known. Metal silicide thin films areintegral parts of all microelectronics devices. For electronic devices,they are typically produced by depositing a metal source on siliconfollowed by thermal treatments. The refractory metal silicides have beenused as ohmic contacts, Schottky barrier contacts, gate electrodes,local interconnects, transistors, and diffusion barriers. With advancesin semiconductor device fabrication technology, the shrinkage inlinewidth continues at a fast pace. Thus, an improved method for thecontrolled synthesis of metal silicide nanoparticle compositions isneeded. In addition, metal silicides are vacuum deposited as film onhigh temperature engine components to improve specific properties.

Refractory metal silicides are currently used in numerous hightemperature applications including the semiconductor industry,aerospace, and for their catalytic activities in chemical reactions andenergy related uses. The disilicides of molybdenum and tungsten were thefirst to be used in metal-oxide-semiconductor (MOS) devices, whichresulted in the rapid development and applications of silicides as gateand interconnects in integrated circuits. Though metal like in theirphysical properties, silicides are in general brittle at roomtemperature. Each silicide has its own specific properties for usage inapplications under extreme environment conditions. Several metalsilicides including MoSi₂, WSi₂, TaSi₂, TiSi₂, and NbSi₂ have beenimplemented in various MOS devices and circuits. The low electricalresistance of silicides in combination with high thermal stability,electron-migration resistance, and excellent diffusion barriercharacteristics is important for microelectronic applications. Over thepast 30 years, metal silicides have been widely used in dense,high-performance, very large scale integration (VLSI) and ultra-largescale integration (ULSI) CMOS integrated circuits. This is due to thefact that the use of silicides allows for the formation of lowresistance source, gate, and drain contacts, which can significantlyreduce the resistance of a CMOS gate conductor and/or the source/drainseries resistance drive current. The lower resistance of the metalsilicides contact gives improved device performance in terms ofswitching speed or source/drain drive current. There is a real need forthe development of nanoparticle refractory metal silicides as theminimization of transistors and other electronic components continues toimprove speed.

Films, fibers, and powders of these ceramics have not typically beenproduced in the presence of a support material such as carbon orpolymeric precursors. Refractory structural metal silicides aretypically prepared by powder metallurgy methods such as hot presssintering. Ordinarily, metal silicide ceramics made by these techniques,which are both energy and time intensive, result in brittle materials,owing partly to the large granular structure and the inconsistently inthe metal silicide particle sizes. Refractory metal silicides offer abalance of room, low, intermediate and high (<1400° C.) temperatureproperties and are candidates to replace Ni based superalloys in futuregas turbine engines. The drive toward advanced high thrust-to-weightratio propulsion systems requires the development of high strength andlow-density structural materials capable of extended operation attemperatures as high as 1600° C. Intermetallics such as nickel andtitanium aluminides have been extensively studied. These intermediateshave melting temperatures of 1400-1600° C., which limits their maximumtemperatures to about 1200° C. Intermediate-based compound materialssuch as Nb and Mo silicides have been combined with metallic secondphases in order to generate composites with a combination of attractivelow-temperature properties. Niobium silicide-based in situ compositeswith Nb₃Si and/or Nb₅Si₃ silicides have been shown to have greatpotential because of their attractive balance of high- andlow-temperature materials. Molybdenum disilicide (MoSi₂) is a highmelting point (2030° C.) material with excellent oxidation resistanceand a moderate density (6.24 g/cm³), which is used in high temperaturefurnaces because it can withstand prolonged exposure in air. It is apromising candidate material for high temperature structuralapplications, particularly in aircraft gas turbine engines. Molybdenumdisilicide-based composites have emerged as important elevatedtemperature structural materials for applications in oxidizing andaggressive environments. Current applications of MoSi₂-based compositesinclude turbine airfoils, combustion chamber components in oxidizingenvironments, missile nozzles, industrial gas burners, diesel engineglow plugs, and materials for glass processing. With its high meltingpoint and excellent high temperature oxidation resistance, MoSi₂ is alsocommonly used as heating elements and can be used for temperatures up to1800° C. in electric furnaces used in laboratory and productionenvironments in the production of glass, steel, electronics, ceramicsand in heat treatment of materials. While the elements are brittle, theycan operate at high power without aging, and their electricalresistivity does not increase with operation time.

There is current interest in metal silicides with small particle sizeand high surface area due to their potential application as catalysts.Refractory metal silicides are used as catalysts due to their oxidativeresistance in the generation of hydrogen and/or oxygen with or withoutlight but are more efficient when run under radiation. Thus, they arecandidates for fuel cells for the automotive industry. Smaller sizeparticles should be more reactive and more efficient for thisapplication. Hydrogen and oxygen evolution from water usingsemiconductors and light is an important issue in the exploitation ofsolar radiation as a sustainable energy. However, a major drawback ofmost of the research in this field relates to the fact that appropriatesemiconductors either are not readily accessible, absorb solar radiationinefficiently, or produce hydrogen while being degraded. A number of therefractory metal silicides are showing promise because of excellentresistance to oxidation at high temperature and high electricalconductivity. The silicides are found to absorb sufficient solar orartificial radiation by themselves without any surface engineering. Inaddition, the water purity or quality is of minor importance for theoxidation and reduction reaction and storing/absorbing andreleasing/desorbing hydrogen and oxygen. The release/desorption ofhydrogen and oxygen can occur at ambient temperatures especially therelease of hydrogen but is more favorable at elevated temperatures.

Refractory metal silicide ceramic parts, forms, and other shapes can befabricated from transition metal silicides powders under extremely highpressure and at high temperatures (>2000° C.), a process known as hotpress sintering. The powdered metal silicides themselves are synthesizedindependently from metal particles or metal compounds and silicon orsilicon salts. As prepared, the sintered refractory ceramics are brittledue to the granularity of the individual particles sticking together.

BRIEF SUMMARY

Disclosed herein is a composition comprising: nanoparticles comprising arefractory-metal silicide; and a carbonaceous matrix. The composition isnot in the form of a powder.

Also disclosed herein is a composition comprising: a metal component,elemental silicon, and an organic component. The metal component isselected from: nanoparticles or particles of a refractory metal; and arefractory-metal compound capable of decomposing into refractory-metalnanoparticles. The organic component is selected from: an organiccompound having a char yield of at least 60% by weight; and a thermosetmade from the organic compound.

Also disclosed herein is a method comprising: combining particles of arefractory metal or a refractory-metal compound capable of decomposingor reacting into refractory-metal nanoparticles, elemental silicon, andan organic compound having a char yield of at least 60% by weight toform a precursor mixture.

Also disclosed herein is a method comprising: providing a precursormixture of particles of a refractory metal or a refractory-metalcompound capable of decomposing into refractory-metal nanoparticles,elemental silicon, and an organic compound; heating the precursormixture in an inert atmosphere at an elevated pressure at a temperaturethat causes decomposition of the refractory-metal compound to formrefractory-metal nanoparticles to form a metal nanoparticle composition;and heating the metal nanoparticle composition in an inert atmosphere,argon, nitrogen, or vacuum at a temperature that causes formation of aceramic comprising nanoparticles of a refractory-metal silicide in acarbonaceous matrix. The organic compound has a char yield of at least60% by weight when heated at the elevated pressure

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation will be readily obtained by reference tothe following Description of the Example Embodiments and theaccompanying drawings.

FIG. 1 schematically illustrates a process for forming the disclosedcompositions.

FIG. 2 schematically illustrates metal and silicon particles 10 embeddedin a thermoset matrix 20.

FIG. 3 schematically illustrates the transfer 40 of silicon and carbonatoms from the carbon matrix 30 to the transition metal 50.

FIG. 4 schematically illustrates metal silicide nanoparticles 60 in acarbonaceous matrix 70.

FIG. 5 shows an X-ray diffraction analysis (XRD) of a sample containingZrSi₂ nanoparticles in a silicon matrix.

FIG. 6 shows an XRD of a sample containing TiMoSi₂ nanoparticles in asilicon matrix.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth in order to provide athorough understanding of the present disclosure. However, it will beapparent to one skilled in the art that the present subject matter maybe practiced in other embodiments that depart from these specificdetails. In other instances, detailed descriptions of well-known methodsand devices are omitted so as to not obscure the present disclosure withunnecessary detail.

Disclosed herein are (1) a method for the in situ formation ofnanoparticle refractory metal silicides (Groups IV-VI) namely Ti, Zr,Nb, Mo, Hf, Ta, and W with a trace or a minute quantity of a carbonsource from meltable polymer in one step affording a shaped compositionwith structural integrity, (2) various refractory metalprecursor-silicon/thermoset compositions, (3) metal-silicide-metalcarbide-silicon carbide nanoparticle compositions at multiple stages,and (4) fiber reinforced metal-silicide and metal silicide-metalcarbide-silicon carbide carbon nanoparticle composites. The refractorymetal silicides are synthesized in situ in any shape or form desired inone step by thermal means. Moreover, hybrid silicides can also besynthesized by the innovative method involving the uses of more than onerefractory metal source in any precursor composition. To improve on thestructural integrity and isolation of the metal silicide nanoparticles,a small amount of 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) is addedto the precursor composition. Many of the materials, methods, andparameters disclosed in U.S. Pat. Nos. 8,822,023; 8,865,301; 8,815,381;and 8,778,488 may be used in the present method, as appropriate.

In the methods disclosed herein, metal compounds and silicon can becombined with a carbon precursor, such as TPEB. Trace to minutequantities of TPEB can be used which will affect the composition of theresulting metal silicide and other ceramic components within the shapedsolid ceramic composition. To obtain high yields of metal silicide, atrace amount of the TBEB is preferred to behave as a binder for thenanoparticle metal silicide and to minimize the formation of the metalcarbide and/or silicon carbide. The unsaturation (ethynyl groups) ofTPEB permits the carbon precursor to undergo conversion from the melt toform thermosets or crosslinked polymers with the metal source andsilicon powder embedded homogeneously within the confines of the solidthermoset. To directly obtain a shaped metal silicide ceramic component,the precursor composition is subjected to pressure and/or vacuum andheated to temperatures in excess of 250° C. causing curing of the TPEBand the shaped solid. A typical composition includes the metal compoundor multiple metal compounds, silicon powder, and the carbon precursor.Upon heating this composition, the carbon precursor melts at its meltingpoint and is thermally converted to a shaped solid thermoset throughreaction of the unsaturated sites. It is possible that during this stepthe metal compound thermally decomposes into metal nanoparticles, whichare embedded in the solid thermoset. Alternatively, the formation of themetal nanoparticles may occur later during the next step in the process,which is extended heat treatment at higher temperatures. Thermaltreatment of the thermoset above 500° C. results in carbonization of thecarbon precursor and reaction of the metal source and silicon. A traceamount of carbon ensures the formation of mainly refractory metalsilicide. However, the amount of metal silicide, metal carbide andsilicon carbide within the resulting composition can be varied based onthe quantity of each individual component (metal compound, silicon, andmelt processable carbon compound) mixed for usage in the precursorcomposition.

A synthetic method has been developed to produce refractory metal (Ti,W, Nb, Zr, Mo, Cr, V, Ta, and Hf) silicides in shaped solidconfigurations from metal particle or metal nanoparticles. Mixed phasescan also be produced. The metal silicides are produced as nanoparticlesin an excess or only a trace amount of carbon precursor. Research showsthat when (a) any refractory metal powder or refractory metal compoundthat decomposes into highly reactive metal particles or metalnanoparticles is combined with (b) silicon powder in either a trace orexcess amount of carbon precursor, the combination can be thermallyconverted to (c) a solid shape containing high yields of pure metalsilicides and/or metal silicides and metal nitrides. When the carbonprecursor is present in excess, metal silicides, metal carbide, andsilicon carbide are also possible as products. The appropriate metalparticles or metal nanoparticles can be formed in situ from the thermaldecompositions of metal hydrides within the confines of the silicon andcarbon precursor. The carbon sources are melt processablearomatic-containing acetylenes or low molecular weight polymers thatexhibit extremely high char yields. The carbon precursor contains only Cand H to insure that heteroatoms are not incorporated into theinterstitial sites of the metal nanoparticles during the reaction toproduce the metal carbide and/or metal nitride. The metal silicides ormetal nitrides form between 600-1500° C. under inert conditions fromreaction of the highly reactive metal particles with either the siliconand/or carbon precursor (degradation above 500° C.) in an atmosphere ofargon or nitrogen gas, respectively, but in some cases the reaction canbe made to occur faster at higher temperatures. The temperature ofchoice used will depend on the reactivity of the metal toward silicon.When an excess or trace of the carbon precursor is used, the individualformed metal silicide ceramic nanoparticles are glued or bound togetherwith the resulting nanostructured or amorphous elastic carbon to affordstructural integrity. The carbon also isolates the nanoparticle metalsilicides to reduce aggregation or agglomeration into larger particlesizes.

The process is outlined in FIG. 1 and schematically illustrated in FIGS.2-4. Any reactions described are not limiting of the presently claimedmethods and compositions. It is speculated that the nanoparticle form ofthe refractory metal activates its reaction with the silicon and carbonsource, thereby lowering the temperature of metal silicide formation.Moreover, by varying the amount of metal compound that forms reactivemetal nanoparticles relative to the silicon and carbon precursor, theamount of metal silicide, metal carbide, and/or silicon carbide can bechanged with respect to the amount of carbon matrix in order to vary theproperties of the resulting composition. The amount of metal carbideand/or silicon carbon is dependent on the amount of the carbon precursorpresent in the original precursor composition. In the case where only atrace amount of carbon precursor is used, metal silicide formation woulddominate the ceramic nanoparticle composition in a shaped solid. Themetal silicides (trace amount of carbon matrix) or metal silicide, metalcarbide, silicon carbide, and/or carbon-matrix compositions are expectedto show enhanced toughness, owing to the presence of the relativelyelastic carbon even when present in trace amounts, which would exist informs ranging from amorphous to nanotube to graphitic carbon.

The inclusion of varying amounts of boron into the precursor compositioncontaining a refractory metal source, silicon or silicon-containingmaterials, and boron in the carbon source material may permit theformation of boride or silicide transition refractory metal ceramics,which are also extremely important in high temperature applications andthe semiconductor industry. Such formation of metal borides is disclosedin U.S. Pat. No. 8,865,301.

In the first step of the method, three components are combined and maybe thoroughly mixed. The first component is a metal component which maybe a refractory-metal compound capable of decomposing into refractorymetal nanoparticles or particles of a refractory metal. Any refractorymetal may be used, including but not limited to a group IV-VI transitionmetal, titanium, zirconium, hafnium, tungsten, niobium, molybdenum,chromium, tantalum, or vanadium. More than one metal may be used. When apure metal is used, it may be in the form of nanoparticles or otherparticles such as a powder. When such metal particles are used, themetal may directly react with the organic component. Suitable powdersinclude, but are not limited to, tungsten and tantalum.

Instead of pure metal, a compound containing the metal atom may be used.Such compounds decompose at elevated temperatures, releasing the metalatoms so that they may react with the organic component. Suitable suchcompounds include, but are not limited to, a salt, a hydride, a carbonylcompound, or a halide of the refractory metal. Examples include titaniumhydride, zirconium hydride, and hafnium hydride. Other examples andembodiments of types of compounds which may be used with the metalsdisclosed herein may be disclosed in U.S. Pat. Nos. 6,673,953;6,770,583; 6,846,345; 6,884,861; 7,722,851; 7,819,938; 8,277,534.

The second component is silicon in elemental form. Suitable silicon isreadily available in powder form in >99% purity. The silicon powder maybe milled to reduce its particle size. Milling to as small a particlesize as possible may improve the final product.

The third component is an organic compound that has a char yield of atleast 60% by weight. The char yield may also be as high as at least 70%,80%, 90%, or 95% by weight. The char yield of a potential compound maybe determined by comparing the weight of a sample before and afterheating to at least 1000° C. for at least 1 hr in an inert atmospheresuch as nitrogen or argon. Any such compounds with high char yields maybe used as the charring may play a role in the mechanism of thereactions. This char yield may be measured at an elevated (e.g. aboveatmospheric) pressure to be used when a heating step is also performedat such pressure. Thus, a compound having a low char yield atatmospheric pressure but having a high char yield under externalpressure or the conditions that the disclosed methods are performed maybe suitable for producing silicon carbides and silicon nitrides.

Certain organic compounds may exhibit any of the followingcharacteristics, including mutually consistent combinations ofcharacteristics: containing only carbon and hydrogen; containingaromatic and acetylene groups; containing only carbon, hydrogen, andnitrogen; containing no oxygen; and containing a heteroatom other thanoxygen. It may have a melting point of at most 400° C., 350° C., 300°C., 250° C., 200° C. or 150° C. and the melting may occur beforepolymerization or degradation of the compound or it may be a liquid.Examples of organic compounds include, but are not limited to,1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB), 4,4′-diethynylbiphenyl(DEBP), N,N′-(1,4-phenylenedimethylidyne)-bis(3-ethynylaniline) (PDEA),N,N′-(1,4-phenylenedimethylidyne)-bis(3,4-dicyanoaniline)(dianilphthalonitrile), and 1,3-bis(3,4-dicyanophenoxy)benzene(resorcinol phthalonitrile) or a prepolymer thereof. More than oneorganic compound may be used. Prepolymers may also be used, such as aprepolymer of TPEB or other suitable organic compounds. Differentcompounds can be blended together and/or reacted to a prepolymer stagebefore usage as the organic compound of the precursor composition. Thepresence of nitrogen atoms in the organic compound may produce metalnitrides in the ceramic without the use of a nitrogen atmosphere.

An optional component in the precursor materials is a plurality offibers or other fillers. Examples of fibers include, but are not limitedto, carbon fibers, ceramic fibers, and metal fibers. The fibers may beof any dimension that can be incorporated into the mixture and may becut or chopped to shorter dimensions.

Another optional component is boron for formation of silicon boroncarbide nanoparticles. Suitable boron is readily available in powderform. A 95-97% boron is suitable with a higher purity boron powder (99%)being preferred. The boron powder may be milled to reduce its particlesize. The boron may be used in any way disclosed in U.S. Pat. Nos.8,822,023 and 8,865,301.

Also, the precursor mixture, including any fibers, may be formed into ashaped component. The component may be shaped and/or heated underpressure, removed from the pressure, and heated to thermoset and ceramiccomponents as described below. The precursor composition may also bemilled.

The precursor mixture, which may be mixed in a melt stage, thenundergoes a heating step to form a thermoset composition. This may beperformed while the mixture is in a mold. This will allow the finalproduct to have the same shape as the mold, as the organic component ofthe mixture will melt if not already liquid and the mixture will fillthe mold during the heating, and retain its shape when the ceramic isformed. The precursor mixture is heated in an inert atmosphere or vacuumat a temperature that causes polymerization of the organic compound to athermoset. If the organic compound is volatile, the heating may beperformed under pressure, either physical or gas pressure, to avoidevaporation of the organic compound. Suitable heating temperaturesinclude, but are not limited to, 150-500° C. or 700° C.

Heating the precursor may also cause the polymerization of the organiccompound to a thermoset. The silicon and metal particles 10 would thenbe dispersed throughout the thermoset 20 as shown in FIG. 2. A thermosethaving the particles dispersed throughout may be used as a finalproduct. The thermoset may also be machined to a desired shape, followedby heating to form a ceramic as described below.

The silicon and metal may be homogeneously distributed or embedded inthe thermoset as an intermediate shaped solid. At this stage, thecomposition may have a shape that it will retain upon further heatingand conversion to the ceramic from reaction of the silicon with thedeveloping carbon matrix.

The precursor mixture may be consolidated to a shaped solid componentunder pressure to promote intimate contact of the reactants to provide avery dense ceramic solid or to densify the final product. The precursormixture may be compacted under exterior pressure, removed from thepressure, and then heated to a thermoset followed by conversion to theceramic. Alternatively, the precursor mixture may be compacted underexterior pressure and the pressure maintained while heating to thethermoset and ceramic.

Optionally, the thermoset composition may be heated between 600 to 1400°C. The upper end of the range approaches the melting point of silicon.These temperatures may produce carbonization of the organic precursor toproduce a metal-silicon-carbon composition in which the metal andsilicon are embedded in the carbon waiting to react at or above themelting point of the silicon.

In a second heating step, the thermoset composition is heated to form aceramic. The heating is performed at a temperature that causes formationof nanoparticles of metal silicide 60 in a carbonaceous matrix orsilicon matrix 70 (FIG. 4). Metal carbide and silicon carbide particlesmay also be formed. The carbonaceous matrix may comprise graphiticcarbon, carbon nanotubes, and/or amorphous carbon. If nitrogen ispresent, metal nitride nanoparticles may be formed. There may be ahigher concentration of nitrides on the surface than in the interior.Suitable heating temperatures include, but are not limited to 500-1900°C. If boron is present, then silicon boron carbide or metal boridenanoparticles may be formed.

The presence and composition of the nanoparticles may be verified by anyknown technique for detecting nanoparticles such as SEM, TEM, or XRD.The nanoparticles may have an average diameter of less than 100 nm, 50nm, or 30 nm. They may be generally spherical in shape or may benon-spherical, such as nanorods or other nanostructures. As used herein,the term “nanoparticle” also includes nanocrystallites, and may includeparticles larger than 100 nm or larger than 1 micron, or up to 10microns in diameter.

The ceramic may include any amount of nanoparticles and/or nanorods,including but not limited to, at least 5%, 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, 90%, 95%, or 99% by weight of nanoparticles. The percentage ofnanoparticles and/or nanorods may be in part determined by the molarratio of metal, silicon, and carbon atoms in the precursor mixture.

The ceramic is not formed as a powder and may be in the form of a solid,unbroken mass. It may contain less than 20% by volume of voids or as lowas 10%, 5%, or 1%. It may have the same shape as the precursor mixture(if solid) or it may take on the shape of a mold it was placed in duringthe heating. The ceramic may retain its shape in that it does notcrumble when handled and may not change shape or break without the useof extreme force. The ceramic composition may be tough, hard, and havestructural integrity. The degree of such properties may depend on theamount of ceramic to carbon in the solid ceramic composition. Any shapemay be formed to make an article useful for incorporation into anapparatus. The article may be large enough to have a minimum size of atleast 1 cm in all dimensions. That is, the entire surface of the articleis at least 5 mm from the center of mass of the article. Larger articlesmay be made, such as having a minimum size of at least 10 cm in alldimensions. Also, the composition may have smaller sizes, such as 1 mm,2 mm, or 5 mm.

Potential advantages may include the following. 1) The reaction isperformed in situ in one step in any solid shape, form, or film desired.2) Regardless of the ratio of metal compound and silicon powder tocarbon source, the metal silicide and carbide form as nanoparticles:this is a highly desirable result, as it is generally accepted thathomogeneous nanoparticle composites of ceramics will have betterproperties than their much more common microparticle counterparts. 3)The temperatures at which the synthetic process occurs is well belowthose normally associated with the formation of silicide- andcarbide-based ceramics. 4) By its very nature, the method permits thesilicide and/or silicide-carbide-carbon composites to be easily shapedby liquid molding procedures (injection pressure molding, vacuummolding, spreading, etc.), which is a far less costly and involvedprocess than machining a hot press sintered powdered material. 5) Thenative presence of an “elastic” carbon matrix allows for toughening ofthe inherently brittle sintered ceramics. The carbon permits operationof the toughened ceramic at extremely high temperatures, owing tocarbon's high melting point (>3000° C.). Ceramic/carbon-matrixcompositions are currently sought for these reasons, and the presentinvention permits straightforward preparation of these composites in asingle step for the first time, in contrast to the traditional means offirst forming the ceramic powder and then preparing the ceramic shapedsolid composition under sintering conditions. Also, the ratio of ceramicto carbon is easily tuned based only on the ratio of metal-compound tocarbon-precursor. 6) The precursor composition containing the carbonprecursor (for example, TPEB) can be deployed as a thin film by 3Dprintings and the formulation of circuits. 7) Fiber reinforced ceramicnanoparticle composite can be readily fabrication by the method of thisinvention with the presence of the carbon precursor the key.

Carbon fiber-reinforced refractory metal silicides-carbon matrixcomposites or metal silicide, metal carbide, silicon carbide, and/orcarbon-matrix composites may exhibit outstanding mechanical propertiesfor usage under extreme environmental high temperature conditions; thesematerials do not currently exist. Finely divided fiber reinforcedrefractory metal silicide ceramic-carbon composites allow theconsolidation of fully dense shaped solid components with extremefracture resistance for uses in high stress and temperature applicationssuch as advanced engine components for hypersonic vehicles andautomobiles, where increased operation temperature and mechanicalintegrity could translate into tremendous economic advantages. Suchtough, easily shaped ceramic composites are critical to the nextgeneration of jet engines, which are being designed to operate at higherinternal temperatures and stresses than those in current service, and inadvanced automobile engines and supporting components. The rails of arailgun would be improved with hard, high-temperature, conductiveceramic coatings. In addition, high temperature ship deck plates couldbe readily fabricated for aircraft carriers needing the superior heatresistant properties of the metal silicides-carbon matrix composites ormetal silicide, metal carbide, silicon carbide, and/or carbon-matrixcomposites. The ability to fabricate tough, shaped refractory metalsilicides-carbon matrix composites or metal silicide, metal carbide,silicon carbide, and/or carbon-matrix composites in one step enhancestheir importance due to the economic advantages and the elimination ofsintering of the respective powders at high temperature and pressuremachining to a shaped component.

The following examples are given to illustrate specific applications.These specific examples are not intended to limit the scope of thedisclosure in this application.

EXAMPLE 1

Formulation of precursor composition of TPEB, titanium hydride, andsilicon powder (1 to 5 μm particle size) in 0.003 to 1 to 1.9 molarratios—TPEB (28 mg, 0.06 mmol), titanium hydride (1.00 g, 20.0 mmol),and silicon powder (1 to 5 μm particle size) (1.07 g, 38.1 mmol) werethoroughly mixed and used as the precursor composition for the formationof titanium silicide nanoparticles/nanostructures embedded in a matrixof carbon or silicon carbide that behaves as a matrix material. Theratio of the three reactants can be readily varied by the describedformulation method.

EXAMPLE 2

Conversion of precursor composition of TPEB, titanium hydride andsilicon powder (1 to 5 μm particle size) in 0.003 to 1 to 1.9 molarratios to polymeric thermoset solid in an argon atmosphere—A sample (100mg) of the precursor composition of Example 1 was weighed into a TGAceramic pan, packed thoroughly, flushed with flow (110 cc/min) of argonfor 20 minutes, and then heated at 5° C./min to 250° C. and held at thistemperature for 1 hr to consolidate to a shaped thermoset solid fromreaction of the ethynyl units of TPEB.

EXAMPLE 3

Conversion of polymeric thermoset solid to shaped titaniumsilicide-carbide matrix solid ceramic composition by heating to 1500° C.under an argon atmosphere—The solid polymeric thermoset of Example 2 washeated under a flow (110 cc/min) of argon at 3° C./min to 1200° C. andheld at this temperature for 1 min followed by heating at 1° C./min to1415° C. and holding at this temperature for 1 hr and at 1° C./min to1500° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 93% of the original weight. XRD analysis showedthe formation of pure titanium silicide nanoparticles/nanostructuresembedded in a matrix of carbon and/or silicon carbide.

EXAMPLE 4

Formulation of precursor composition of TPEB, titanium hydride andsilicon powder (1 to 5 μm particle size) in 0.03 to 1 to 1 molarratios—TPEB (282 mg, 0.59 mmol), titanium hydride (1.00 g, 20.0 mmol)and silicon powder (1 to 5 μm particle size) (0.560 g, 20.0 mmol) werethoroughly mixed and used as the precursor composition for the formationof titanium silicide nanoparticles/nanostructures embedded in a matrixof carbon or silicon carbide that behaves as a matrix material. Theratio of the three reactants can be readily varied by the describedformulation method.

EXAMPLE 5

Conversion of precursor composition of TPEB, titanium hydride andsilicon powder (1 to 5 μm particle size) in 0.03 to 1 to 1 molar ratiosto polymeric thermoset solid in an argon atmosphere—A sample (100 mg) ofthe precursor composition of Example 4 was weighed into a TGA ceramicpan, packed thoroughly, flushed with flow (110 cc/min) of argon for 20minutes, and then heated at 5° C./min to 250° C. and held at thistemperature for 1 hr to consolidate to a shaped thermoset solid fromreaction of the ethynyl units of TPEB.

EXAMPLE 6

Conversion of polymeric thermoset solid to shaped titaniumsilicide-carbide matrix solid ceramic composition by heating to 1500° C.under an argon atmosphere—The solid polymeric thermoset of Example 5 washeated under a flow (110 cc/min) of argon at 3° C./min to 1200° C. andheld at this temperature for 1 min followed by heating at 1° C./min to1415° C. and holding at this temperature for 1 hr and at 1° C./min to1500° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 93% of the original weight. XRD analysis showedthe formation of pure titanium silicide nanoparticles/nanostructuresembedded in a matrix of carbon and/or silicon carbide.

EXAMPLE 7

Formulation of precursor composition of TPEB, zirconium hydride andsilicon powder (1 to 5 μm particle size) in 0.03 to 1 to 1.9 molarratios—TPEB (15 mg; 0.03 mmol), zirconium hydride (1.00 g, 10.7 mmol)and silicon powder (1 to 5 μm particle size) (0.570 g, 20.3 mmol) werethoroughly mixed and used as the precursor composition for the formationof zirconium silicide nanoparticles/nanostructures embedded in a matrixof carbon or silicon carbide that behaves as a matrix material. Theratio of the three reactants can be readily varied by the describedformulation method.

EXAMPLE 8

Conversion of precursor composition of TPEB, zirconium hydride andsilicon powder (1 to 5 μm particle size) in 0.03 to 1 to 1.9 molarratios to polymeric thermoset solid in an argon atmosphere—A sample (125mg) of the precursor composition of Example 7 was weighed into a TGAceramic pan, packed thoroughly, flushed with flow (110 cc/min) of argonfor 20 minutes, and then heated at 5° C./min to 250° C. and held at thistemperature for 1 hr to consolidate to a shaped thermoset solid fromreaction of the ethynyl units of TPEB.

EXAMPLE 9

Conversion of polymeric thermoset solid to shaped zirconiumsilicide-carbide matrix solid ceramic composition by heating to 1500° C.under an argon atmosphere—The solid polymeric thermoset of Example 8 washeated under a flow (110 cc/min) of argon at 3° C./min to 1200° C. andheld at this temperature for 1 min followed by heating at 1° C./min to1415° C. and holding at this temperature for 1 hr and at 1° C./min to1500° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 93% of the original weight. XRD analysis (FIG.5) showed the formation of pure zirconium silicidenanoparticles/nanostructures with an average crystallite size of 10 nmembedded in a matrix of carbon and/or silicon carbide.

EXAMPLE 10

Formulation of precursor composition of TPEB, hafnium hydride andsilicon powder (1 to 5 μm particle size) in 0.003 to 1 to 1.9 molarratios—TPEB (8 mg; 0.02 mmol), hafnium hydride (1.00 g, 5.54 mmol) andsilicon powder (1 to 5 μm particle size) (0.296 g, 10.5 mmol) werethoroughly mixed and used as the precursor composition for the formationof hafnium silicide nanoparticles/nanostructures embedded in a matrix ofcarbon or silicon carbide that behaves as a matrix material. The ratioof the three reactants can be readily varied by the describedformulation method.

EXAMPLE 11

Conversion of precursor composition of TPEB, hafnium hydride and siliconpowder (1 to 5 μm particle size) in 0.003 to 1 to 1.9 molar ratios topolymeric thermoset solid in an argon atmosphere—A sample (155 mg) ofthe precursor composition of Example 10 was weighed into a TGA ceramicpan, packed thoroughly, flushed with flow (110 cc/min) of argon for 20minutes, and then heated at 5° C./min to 250° C. and held at thistemperature for 1 hr to consolidate to a shaped thermoset solid fromreaction of the ethynyl units of TPEB.

EXAMPLE 12

Conversion of polymeric thermoset solid to shaped hafniumsilicide-carbide matrix solid ceramic composition by heating to 1500° C.under an argon atmosphere—The solid polymeric thermoset of Example 11was heated under a flow (110 cc/min) of argon at 3° C./min to 1200° C.and held at this temperature for 1 min followed by heating at 1° C./minto 1415° C. and holding at this temperature for 1 hr and at 1° C./min to1500° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 92% of the original weight. XRD analysis showedthe formation of pure hafnium silicide nanoparticles/nanostructuresembedded in a matrix of carbon and/or silicon carbide.

EXAMPLE 13

Formulation of precursor composition of TPEB, molybdenum metal andsilicon powder (1 to 5 μm particle size) in 0.006 to 1 to 1.8 molarratios—TPEB (30 mg; 0.06 mmol), molybdenum metal (1.00 g, 10.4 mmol) andsilicon powder (1 to 5 μm particle size) (0.527 g, 18.7 mmol) werethoroughly mixed and used as the precursor composition for the formationof molybdenum silicide nanoparticles/nanostructures embedded in a matrixof carbon or silicon carbide that behaves as a matrix material. Theratio of the three reactants can be readily varied by the describedformulation method.

EXAMPLE 14

Conversion of precursor composition of TPEB), molybdenum metal andsilicon powder (1 to 5 μm particle size) in 0.2 to 1 to 1.8 molar ratiosto polymeric thermoset solid in an argon atmosphere—A sample (155 mg) ofthe precursor composition of Example 13 was weighed into a TGA ceramicpan, packed thoroughly, flushed with flow (110 cc/min) of argon for 20minutes, and then heated at 5° C./min to 250° C. and held at thistemperature for 1 hr to consolidate to a shaped thermoset solid fromreaction of the ethynyl units of TPEB.

EXAMPLE 15

Conversion of polymeric thermoset solid to shaped molybdenumsilicide-carbide matrix solid ceramic composition by heating to 1500° C.under an argon atmosphere—The solid polymeric thermoset of Example 14was heated under a flow (110 cc/min) of argon at 3° C./min to 1200° C.and held at this temperature for 1 min followed by heating at 1° C./minto 1415° C. and holding at this temperature for 1 hr and at 1° C./min to1500° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 95% of the original weight. XRD analysis showedthe formation of pure molybdenum silicide nanoparticles/nanostructuresembedded in a matrix of carbon or silicon carbide.

EXAMPLE 16

Formulation of precursor composition of TPEB, molybdenum metal, titaniumhydride, and silicon powder (1 to 5 μm particle size) in 0.006 to 0.5 to0.5 to 1.8 molar ratios—TPEB (30 mg; 0.06 mmol), molybdenum metal (0.50g, 5.21 mmol), titanium hydride (0.26 g, 5.21 mmol) and silicon powder(1 to 5 μm particle size) (0.527 g, 18.7 mmol) were thoroughly mixed andused as the precursor composition for the formation of molybdenumsilicide/titanium silicide nanoparticles/nanostructures embedded in amatrix of carbon and/or silicon carbide that behaves as a matrixmaterial. The ratio of the three reactants can be readily varied by thedescribed formulation method.

EXAMPLE 17

Conversion of precursor composition of TPEB, molybdenum metal, titaniumhydride, and silicon powder (1 to 5 μm particle size) in 0.2 to 0.5 to0.5 to 1.8 molar ratios to polymeric thermoset solid in an argonatmosphere—A sample (155 mg) of the precursor composition of Example 16was weighed into a TGA ceramic pan, packed thoroughly, flushed with flow(110 cc/min) of argon for 20 minutes, and then heated at 5° C./min to250° C. and held at this temperature for 1 hr to consolidate to a shapedthermoset solid from reaction of the ethynyl units of TPEB.

EXAMPLE 18

Conversion of polymeric thermoset solid to shaped molybdenum/titaniumsilicide-carbide matrix solid ceramic composition by heating to 1500° C.under an argon atmosphere—The solid polymeric thermoset of Example 17was heated under a flow (110 cc/min) of argon at 3° C./min to 1200° C.and held at this temperature for 1 min followed by heating at 1° C./minto 1415° C. and holding at this temperature for 1 hr and at 1° C./min to1500° C. and holding at this temperature for 1 hr. The resulting solidceramic sample retained 95% of the original weight. XRD analysis (FIG.6) showed the formation of pure molybdenum silicide/titanium silicidenanoparticles/nanostructures with an average crystallite size of 95 nmembedded in a matrix of carbon and/or silicon carbide.

Obviously, many modifications and variations are possible in light ofthe above teachings. It is therefore to be understood that the claimedsubject matter may be practiced otherwise than as specificallydescribed. Any reference to claim elements in the singular, e.g., usingthe articles “a”, “an”, “the”, or “said” is not construed as limitingthe element to the singular.

What is claimed is:
 1. A composition comprising: nanoparticlescomprising a refractory-metal silicide; and a carbonaceous matrix;wherein the composition is not in the form of a powder.
 2. Thecomposition of claim 1, wherein the nanoparticles comprise titaniumsilicide, zirconium silicide, hafnium silicide, molybdenum silicide,tungsten silicide, niobium silicide, tantalum silicide, or vanadiumsilicide.
 3. The composition of claim 1, wherein the compositioncomprises at least 5% by weight of the nanoparticles.
 4. The compositionof claim 1, wherein the average diameter of the nanoparticles is lessthan 100 nm.
 5. The composition of claim 1, wherein the compositionfurther comprises: nanoparticles comprising a carbide of the refractorymetal, a nitride of the refractory metal, or silicon carbide.
 6. Anarticle comprising the composition of claim 1, wherein the article is inthe form of a solid, unbroken mass having a minimum size of at least 1mm in all dimensions.
 7. A composition comprising: a metal componentselected from: nanoparticles or particles of a refractory metal; and arefractory-metal compound capable of decomposing into refractory-metalnanoparticles; elemental silicon; and an organic component selectedfrom: an organic compound having a char yield of at least 60% by weight;and a thermoset made from the organic compound.
 8. The composition ofclaim 7, wherein the refractory metal is titanium, zirconium, hafnium,molybdenum, tungsten, niobium, tantalum, or vanadium.
 9. The compositionof claim 7, wherein the metal component is a salt, a hydride, a carbonylcompound, a halide, or particles of the refractory metal.
 10. Thecomposition of claim 7, wherein the organic compound: contains onlycarbon and hydrogen; contains aromatic and acetylene groups; containsonly carbon, hydrogen, and nitrogen; contains no oxygen; or contains aheteroatom other than oxygen.
 11. The composition of claim 7, whereinthe organic compound is 1,2,4,5-tetrakis(phenylethynyl)benzene or aprepolymer thereof.
 12. The composition of claim 7, wherein thecomposition is milled.
 13. A method comprising: combining particles of arefractory metal or a refractory-metal compound capable of decomposingor reacting into refractory-metal nanoparticles, elemental silicon, andan organic compound having a char yield of at least 60% by weight toform a precursor mixture.
 14. The method of claim 13, furthercomprising: milling the precursor mixture.
 15. The method of claim 13,further comprising: placing the precursor mixture into a mold or shapedreactor.
 16. The method of claim 13, further comprising: heating theprecursor mixture in an inert atmosphere or vacuum at a temperature thatcauses decomposition or reaction of the refractory-metal compound orparticles to form refractory-metal nanoparticles to form a metalnanoparticle composition.
 17. The method of claim 16, wherein heatingthe precursor mixture causes polymerization of the organic compound to athermoset.
 18. The method of claim 16, further comprising: heating themetal nanoparticle composition in an inert atmosphere, argon, nitrogen,or vacuum at a temperature that causes formation of a ceramic comprisingnanoparticles of a refractory-metal silicide in a carbonaceous matrix.19. The method of claim 18, wherein heating the metal nanoparticlecomposition causes formation of nanoparticles comprising a carbide ofthe refractory metal, a nitride of the refractory metal, or siliconcarbide.
 20. A method comprising: providing a precursor mixture ofparticles of a refractory metal or a refractory-metal compound capableof decomposing into refractory-metal nanoparticles, elemental silicon,and an organic compound; heating the precursor mixture in an inertatmosphere at an elevated pressure at a temperature that causesdecomposition of the refractory-metal compound to form refractory-metalnanoparticles to form a metal nanoparticle composition; and heating themetal nanoparticle composition in an inert atmosphere, argon, nitrogen,or vacuum at a temperature that causes formation of a ceramic comprisingnanoparticles of a refractory-metal silicide in a carbonaceous matrix;wherein the organic compound has a char yield of at least 60% by weightwhen heated at the elevated pressure.